Soda ash (Na.sub.2 CO.sub.3) is a very high tonnage chemical raw material commonly used in glass making and in the production of sodium chemicals. A large proportion of soda ash is derived from the natural mineral trona, which occurs in great abundance near Green River, Wyo. Chemically, trona is sodium sesquicarbonate Na.sub.2 CO.sub.3.NaHCO.sub.3.2H.sub.2 O. After crushing, the natural ore is dissolved in agitated tanks to form a concentrated solution. Most of the impurities (boron oxides, calcium carbonate silica, sodium silicate, and shale rock) are insoluble in hot H.sub.2 O and separate out upon settling. Upon cooling, the filtered sesquicarbonate solution forms fine needle-like crystals in a vacuum crystallizer. After centrifuging, the sesquicarbonate crystals are heated to about 240.degree. C. in rotary calciners whereupon CO.sub.2 and bound H.sub.2 O are released to form natural soda ash. The crystals have a purity of 99.88% or more and handle easily without abrading or forming dust and thus assisting glassmakers and other users in obtaining uniform and homogeneous mixes.
A critical step in the production of soda ash is the separation of the concentrated soda ash solution from the solid impurities. The current method of separating the soda ash solution from the unwanted solids involves the addition of polymers or natural gums (such as guar gum) to the mixture to help coagulate the solid materials. Very large holding tanks (40 feet high and 110 feet wide) are used to allow the solids to settle over 24-30 hours. The liquid passing over a weir is further processed by filtration in a series of pressure leaf filters packed with diatomaceous earth. Carbon is commonly added to remove additional impurities. The liquid is then evaporated to cause crystallization of the soda ash product.
The solid underflow from the settling tanks is typically reprocessed to recover additional soda ash. Using 2.degree. and 3.degree. reprocessing steps, a typical recovery is from 88% to 93% of the total soda ash.
Current processing steps require high pressure pumps (75 psi) for the pressure leaf filters which consume large amounts of energy to operate. Current processing steps also require large holding tanks. Diatomaceous earth and carbon must be continuously purchased for use in the filtering and purification process.
It would be a significant advancement in the art to provide a process and system which efficiently separates soda ash solution from solid impurities such that 2.degree. and 3.degree. reprocessing is not necessary.
It would be a major advancement in the art to provide a process and system for separating soda ash solution from solid impurities which does not require large holding tanks and related land areas.
It would be a further advancement in the art to provide a process and system for separating soda ash solution from solid impurities which does not require the continual purchase of diatomaceous earth or carbon.
Such processes and systems are disclosed herein.